A modern convenience enjoyed by most consumers is the ready availability of hot water for cooking, cleaning, and personal hygiene. To ensure an adequate supply of such hot water, many dwellings and commercial establishments utilize an electric water heater that includes a large water storage tank or reservoir in which are positioned electrical heating elements and temperature sensors. The water temperature to which the water heater heats and maintains the water temperature may be set by the consumer and is thereafter regulated by an onboard controller.
While smaller electric water heaters may only include a single heating element, many larger water heaters include two electrical heating elements vertically spaced apart from one another within the storage tank. To conserve space, most electric water heaters are configured as a cylindrical tank whose height greatly exceeds its diameter. In such a configuration, the electrical heating elements are typically spaced at two different vertical locations within the storage tank. In such a configuration, two temperatures sensors are typically used, and are placed above and proximate each heating element. As such, the individual temperature sensors can determine the localized temperature of the water proximate the individual heating elements.
Unfortunately, a significant problem that may occur with such electric water heaters is known as a dry fire condition. In a dry fire condition, the electrical heating elements are energized without being submerged in water, i.e. energized at a time when the water heater's storage tank is not filled. The design and construction of such electrical heating elements, however, can not withstand extended periods of energization without being submerged in water. Indeed, typically 10 seconds or longer of energization without being submerged will result in the electrical heating element reaching abnormally high temperatures that are significantly above standard operating temperatures experienced when the heating elements are submerged in water. These high temperatures are reached because no water is present to dissipate the heat generated by the heating elements as would occur when the hot water tank is filled with water.
As a result of these high temperatures, the electrical heating elements rapidly degenerate, and the useful life of the heating element is substantially reduced. It has been noted that energization in a dry fire condition for as little as 30 seconds may result in permanent failure of the heating element. Unfortunately, the occurrence of such situations is not uncommon, particularly during the installation of a new hot water heater if the installation personnel turns on the power to the hot water heater prior to completely filling the storage tank thereof.
In recognition of the serious nature of such a problem and the cost of replacing the heating elements, several approaches have been designed to preclude operation of the hot water heater if a dry fire condition would result. While water level sensors or other mechanisms could be employed to ensure the tank is full before energizing the electrical heating elements, the inclusion of such additional sensors and circuitry would drive up the cost of the hot water heater. This is unacceptable in the highly competitive consumer and commercial appliance market.
As such, many manufactures attempt to sense and prevent operation in a dry fire condition by utilizing the sensors required for normal operation of the hot water heater. These methods include utilizing the internal temperature sensors to sense the temperature proximate each heating element or temperature rise associated with each electrical heating element upon energization thereof. To limit the amount of damage that may be sustained to the electrical heating element until the onboard controller can determine that a dry fire condition exists, some methods utilize a pulse energization of the heating element. However, even in such systems damage to the electrical heating elements occur as the duration of energization must be sufficient to allow the temperature sensors to register a rise in temperature or other required parameter to allow the controller to differentiate a dry fire condition from a normal operating condition.
In view of the above, there exists a need in the art for a method of detecting a dry fire condition without stressing the electrical heating elements as part of the determination. Embodiments of the present invention provide such methods.